*Preparations for Foaling-Facilities, Preparations for Foaling-Caslicks Removal
Inducing Parturition?
*Parturition-Stage I, Parturition-Stage II, Parturition-Stage III
Gestation Length
The average gestation length (duration of pregnancy) of mares is 335 to 340 days, but
can range from 320 to 370 days. There may be much variability among mares, but most
individually follow similar patterns year after year. Foals are considered premature if
delivered at less than 326 days of gestation and usually require immediate veterinary
attention. Mares foaling before 310 days are considered to have aborted. Many
breeders will calculate the expected foaling date at 11 months following the last breeding
date. Most mares will gestate longer than 11 months; however, this allows for fewer
"surprise" foalings in undesirable conditions.
There are various traits which can influence length of a mare's pregnancy. Studies have
shown colts tend to gestate 2 to 7 day longer than fillies. The nutritional plane of a mare
also has been shown to have some influence on gestation length. Additionally, mares
foaling during the late spring and summer months (long days) tend to have a shorter
gestation length than those foaling in January or February. Exposure of bred mares to
artificially lengthened days during the latter third of gestation has been shown to shorten
gestational length by about 10 days.
Early Signs
The signs of impending parturition are about as variable as gestation length. Although
there is a tremendous amount of variation among mares, many individuals do repeat
their foaling behavior year after year. Therefore, it is recommended to keep accurate
records on each mare to aid future deliveries.
The classical signs of approaching parturition include udder development beginning 2 to
6 weeks before foaling, then milk let down into the teats (teat distension) 4-6 days prior
to parturition. Due to oozing out of some of the colostrum, the ends of the teats become
covered over and the mare is said to be "waxing", which occurs 1-2 days before foaling.
At this time, some mares will have occasional dripping or streaming of colostrum
use with the newborn foal. In addition to changes associated with the mammary gland,
muscular relaxation in the pelvic region occurs progressively during the last 7-14 days of
gestation and the mare's vulva begins to relax during the final days of gestation.
Many mares will show these "classic" signs of approaching parturition and make it fairly
easy to determine their foaling time. On the other hand some mares will break all the rules
and these signs may not be present, or may appear at varied times.
Predicting Foaling Time-Water Hardness Test
For mares with unknown foaling history, or for mares which are unpredictable for some
reason, there is help available. Several commercial kits to estimate foaling time have
recently come onto the market. These test kits are based on the fact that in most mares,
calcium and magnesium concentrations in prepartum mammary secretion rise progressively
during the latter portion of gestation to the time of foaling. A majority of mares show a
significant rise in calcium and magnesium concentration just prior to parturition. This allows
foaling attendants to estimate time of foaling within 12 to 24 hours.
The kits have been most useful in determining when the mare will not foal. In other words,
if the test shows no changes in the calcium concentration, the mare probably will not foal
within the next 24 hours, and thus would not need to be watched as closely. When a rise in
calcium is indicated, the foaling attendant could then direct more attention to the mare
which is close to foaling.
These test kits, available from veterinarians, are simple to use and fairly inexpensive (.25 to
$1.00 per test). All kits require taking 1-4 cc; of milk daily once the classical signs of
approaching parturition are observed. Generally, samples should be taken for
approximately 10 days. Recent research has shown daily samples collected during the
early evening hours were adequate for detecting the prepartum calcium rise.
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